1. Field of the Invention
This invention concerns a projector for combining several light beams to project images on a projection surface, and in particular, an apparatus and method capable of correcting focusing error and magnification error on a projection surface.
2. Description of the Prior Art
A conventional liquid crystal color projector forms images of three primary colors on three liquid crystal panels, and the images are superimposed on a screen. In this type of liquid crystal color projector, light beams of each color are combined by means of a dichroic prism or a dichroic mirror, and the combined light beam is projected on a screen by a single projecting lens.
In such a projector, wherein images of different colors on separate liquid crystal panels are superimposed, the images of each color may not coincide properly on the screen due to assembling errors.
Such errors can be prevented by increasing the precision of each optical device in the assembly, or by correcting the errors by performing adjustments after assembling. In the former method, however, the optical devices are more costly and the assembling process is more difficult, so in general the latter method, i.e. adjustment after assembling, is employed.
The focusing error of the whole image can be corrected by adjusting the projecting lens or the screen disposed in the common part of the optical paths.
However, if there are relative focusing errors, magnification errors or other errors in the images, the optical system must be adjusted independently for each color.